1. Field of the Invention
The present invention relates to a dynamic voltage pump circuit, and more particularly, a dynamic voltage pump circuit for increased efficiency at low output voltages and a method thereof.
2. Description of the Prior Art
As today's applications for electronic systems grow at ever-increasing rates, the demand for more efficient energy performance is never ceasing. One such circuit providing power to electronic systems is the voltage pump.
Voltage pumps are circuits that generate a voltage larger than the supply voltage from which they operate. Voltage pumps are key circuits in such applications as Electrically Erasable Programmable Read-Only Memory (EEPROM) and flash memory devices. These devices normally operate at low voltages, but require high voltage pulses to erase existing data from memory cells before they can be written with new data. The higher voltage needed to erase the memory cells is generated internally with an on-chip voltage pump.
While voltage pump circuits are capable of efficiencies sometimes as high as 90-95%, this means that there is at least a 5% wasted energy overhead for operating a voltage pump. Furthermore, a single-stage voltage pump is limited to providing an external supply voltage of at most twice its input supply voltage; to achieve external supply voltage in multiples higher than two, consecutive stages of voltage pumps are necessary. For instance, to provide an external supply voltage capable of four times the input supply voltage (as shown in the related art depicted in FIG. 1), a two-stage voltage pump circuit is implemented: a first stage 110 doubles the input supply voltage, whereas a second stage 120 doubles the already-doubled intermediate supply voltage. The limiter 130 provides a signal to control both the first and second stages 110, 120. Because each stage of a voltage pump has (1190, 120) an inefficiency overhead, having more stages in a voltage pump 100 reduces the overall efficiency of the voltage pump 100.